MRI快速扫描技术在儿童先天性心脏病诊断中的应用

目的:探讨MRI半傅立叶采集单次激发快速SE(HASTE)序列、真稳态进动快速成像(TrueFISP)序列和并行采集技术在儿童先天性心脏病诊断中的应用价值.方法:对50例经超声心动图检查的先天性心脏病患儿进行心脏大血管MRI检查,其中26例行DSA检查,全部病例经手术证实.扫描序列包括HASTE、TrueFISP序列以及回顾性心电门控心血管电影成像,并加用并行采集技术.分析各序列MRI图像质量,并将MRI检查结果与超声心动图、DSA结果进行对照.结果:MRI共检出10种复杂先心共181处心血管畸形.26例行DSA检查共检出畸形120个并均与手术结果吻合,MRI显示畸形114个(95.00%),超声心动图检出畸形110个(92.67%).TrueFISP序列和HASTE序列利于显示血管畸形,电影序列有助于检出心内外分流.结论:HASTE黑血技术、TrueFISP亮血技术结合快速电影序列进行心脏MRI检查,可以获得高质量的图像以及较高的病变检出率,适用于儿童先天性心脏病的诊断.     

MR-Tomographie des Herzens

The introduction of magnetic resonance (MR) tomography has fundamentally changed radiological diagnosis for many diseases. Invasive digital subtraction angiography has already been widely replaced by noninvasive MR angiography for most of the vascular diseases. The rapid technical development of MR imaging in recent years has opened new functional imaging techniques. MR imaging of the heart allows simultaneous measurement of morphological and functional parameters in a single noninvasive examination without any radiation exposure. Because of the high spatial resolution and the reproducibility cine MR imaging is now the gold standard for functional analysis. With the improvement of myocardial perfusion and viability studies many diseases of the heart can be diagnosed in a single examination. MR spectroscopy is the only method which allows a view of the metabolism of the heart. New examinations for vascular imaging and flow quantification complete the goal of "one-stop-shop" imaging of the heart. MR imaging is the only diagnostic modality which allows a complete evaluation of many diseases of the heart with one technique, basic examination as well as follow-up studies. The very rapid improvement in MRI will overcome most of the limitations in the near future, especially concerning MR coronary angiography.     

Functional evaluation of the heart with magnetic resonance imaging

This review examines the capability of cine MRI for evaluation of cardiovascular function and shows early results in valvular, ischemic, and congenital heart disease. MR assessment of left and right ventricular volumes is independent of geometrical models; dimensional values have been defined for normal individuals. Noninvasive measurement of peak and end systolic pressure along with cine MR imaging can be used to calculate left ventricular meridional wall stress which can be used for monitoring of myocardial diseases and evaluation of therapeutic intervention. Cine MR may be more accurate than angiography for identifying regional LV dysfunction since it can measure wall thickening as well as inward wall motion. Regurgitant jets due to valvular lesions are readily seen and their characteristics may be used to define the severity of aortic or mitral regurgitation. Calculation of the regurgitant volume separates patients with mild, moderate, or severe disease. Likewise, the shunt flow across ventricular and atrial septal defects has been visualized in cine MR images and shunt flow calculated. Cine MRI serves as a three-dimensional imaging technique with high temporal resolution. It extends the capability of MRI in cardiac disease beyond the depiction of anatomy and renders a comprehensive cardiac imaging technique for quantitation of cardiac anatomy and function.     

Improved reproducibility in measuring LV volumes and mass using multicoil breath-hold cine MR imaging

There is a generally recognized need for improvement in quality of fast cardiac MR images. Consequently, breath-hold cine MR images were obtained with multiple surface coils connected to phased array receivers, and C/N, intra-observer and inter-observer variabilities for LV volumes and mass were evaluated. Two sets of short-axis images of the LV, one with multiple surface coils and another with a body coil, were acquired in eight subjects with a fast cine MR sequence using k-space segmentation (TR/TE=7/2.2 msec, temporal resolution=56 msec). C/N with multicoil imaging was 32.2 ± 7.6 (mean ± SD), significantly higher than that with a body coil (11.0 ± 3.3, P < .01). The mean percentage differences in intra-observer and inter-observer measurements with multicoil imaging were significantly better than those with a body coil. In conclusion, multicoil imaging provides significant gain in C/N on breath-hold cine MRI of the heart. In addition, intra-observer and inter-observer reproducibilities are improved with multicoil imaging.     

Fast magnetic resonance imaging of the heart.

Fast MR imaging techniques have multiple applications for evaluation of cardiac disease. Cine MRI and MR tagging have been shown to be highly accurate and reproducible in evaluating regional and global myocardial function. Segmented k-space cine MRI and echo-planar imaging (EPI) can considerably improve time efficiency and thereby the clinical utility of these techniques. Double IR fast spin-echo sequences enable breath-hold acquisition of T2 weighted MRI with good suppression of the blood signal. Myocardial perfusion can be assessed with fast dynamic MRI after administration of contrast media. Multi-shot EPI improves temporal resolution and also provides full coverage of the left ventricle. Substantial progress has been made in respiratory gated 3D coronary artery MR angiography with navigator echoes. The newer approaches for coronary arterial imaging including breath-hold three-dimensional segmented EPI and high resolution spiral MRI may further improve clinical usefulness of coronary MR angiography. Assessment of coronary blood flow and flow reserve with phase contrast MRI has the potential for the non-invasive evaluating of the presence and significance of stenosis in the native coronary artery and bypass grafts. Fast cardiac MRI may emerge as a cost effective modality for comprehensive assessments of both cardiac morphology, function, blood flow and perfusion.     

先天性心脏病复杂畸形的增强磁共振血管造影与X线心血管造影的影像对比研究

目的 评估动态增强磁共振血管造影（DCE－MRA）诊断先天性心脏病（先）复杂畸形的临床价值。材料与方法 ２８例先心复杂畸形和大血管形患者术同时接受ＤＣＥ－ＭＲＡ、平发和／或电影以及Ｘ线心血管造影（ＣＡＧ）检查,对ＤＣＥ－ＭＡＲ原始图像进行最大信号强度投影法（ＭＩＰ）和多轴位重建法（ＭＰＲ）重建处理,以手术病理发现为基础,将ＭＲ图像与ＣＡＧ进行诊断价值对比,并进行统计学处理。结果 ＤＤＣＥ－ＭＲＡ所获取的图像对比鲜明,靶血管轮廓清晰,其 显示心脏及大血管的形态和空间分布的能力与ＣＡＧ具有很好的一致性,相关系数r=0.88。２种检查方法均能良好地显示心脏、大血管病变,DCE-MRA发现变病能力略优于ＣＡＧ,两者显示病变符合率达９３％。结论 ＤＣＥ－ＭＲＡ检查安全、无创,与ＣＡＧ一样能显示复杂的、多部位的病变,是一种非常有价值的影像学检查手段,有望部分替代常规血管造影而成为一种新的检查方法。     

Contributions of newer MR imaging strategies for congenital heart disease.

Magnetic resonance (MR) imaging is a valuable noninvasive adjunct in the evaluation of congenital heart disease (CHD). With its multiplanar image acquisition, good spatial resolution, and large-field-of-view image display, MR imaging can allow appreciation of vascular connections not readily apparent at echocardiography or angiography. Evaluation of CHD with MR imaging has two components: definition of cardiovascular anatomy and characterization of blood flow. However, the variety of MR imaging options is large and often confusing. Besides spin-echo and gradient-echo imaging, MR imaging techniques for evaluation of CHD include MR angiography, cine MR imaging, and flow quantification. An understanding of the potential MR imaging options enables formulation and more efficient application of MR imaging strategies. When performed well, MR imaging greatly enhances surgical planning and can even obviate cardiac catheterization. MR imaging is also an excellent modality for serial evaluation of surgical results and complications in cases of CHD.     

MR imaging and CT evaluation of congenital pulmonary vein abnormalities in neonates and infants

Magnetic resonance (MR) imaging and computed tomography (CT) are increasingly being used in diagnosis and follow-up of congenital pulmonary vein anomalies in neonates and infants. Such anomalies include total or partial anomalous pulmonary venous return, sinus venosus defect, malposition of the septum primum, cor triatriatum, pulmonary vein atresia or stenosis, and abnormal number or course of the pulmonary veins. MR imaging provides a wealth of anatomic and functional data that are valuable in case management and planning intervention. Gadolinium-enhanced MR angiography is the mainstay of anatomic evaluation. Ventricular volumetry with two-dimensional steady-state free-precession sequences and flow analysis with cine phase-contrast imaging provide physiologic information that may be used to calculate the degree of right heart enlargement and the shunt fraction, allowing the cardiologist to determine the functional importance of the lesion. CT provides superior spatial resolution and short imaging times but at the expense of exposure to ionizing radiation.     

儿童先天性心脏病心血管造影检查技术

目的 探讨和评价儿童先天性心脏病心血管造影技术。方法 11045例儿童先天性心脏病患者做了心血管造影检查,采用的设备包括早期的快速换片心血管造影设备,电影心血管造影设备和数字减影心血管造影设备。使用了不同的心血管造影技术。结果 用快速换片心血管造影设备和常规正侧位投照时的儿童先天性心脏病心血管造影诊断符合率为80．5％,用电影心血管造影设备和轴位成角投照技术时的造影诊断符合率为90．0％,采用数字减影心血管造影设备,轴位成角投照技术和非离子型对比剂时的造影诊断符合率为96．5％。结论 对于儿童先天性心脏病心血管造影而言,使用动态电影摄片,作数字血管减影,采用轴位成角投照技术,使用非离子型对比剂和快速注射对比剂是取得高质量图像和理想诊断效果的关键。     

MR imaging of aortic coarctation

Aortic coarctation accounts for 5%–10% of all congenital heart diseases and represents 7% of critically ill infants with heart disease. Magnetic resonance (MR) imaging allows the study of this disease with several advantages in comparison with conventional angiography, transesophageal echocardiography, and computed tomography. The MR protocol applied at our institution for both diagnosis and follow-up after surgical or endovascular treatment consists of four steps: morphologic study, cine MR study, flow analysis, and MR angiography (MRA). The first three sequences are acquired during breath-hold and with electrocardiographic gating. Anatomy is well depicted with dark-blood half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences. Cine true-fast imaging with steady-state precession (true-FISP) sequences show not only morphologic features but also blood-flow changes inside the aorta. Gradient-echo sequences for phase-velocity mapping allow flow analysis. Application of Bernoulli’s equation — here briefly presented and discussed — allows for calculation of the pressure gradient caused by the coarctation. MRA, acquired with a breath-hold three-dimensional T1-weighted gradient-echo sequence and intravenous administration of paramagnetic contrast material, allows for optimal depiction of the aortic lumen, with a panoramic view of the whole aorta, its main branches and possible collateral circulation.     

复杂先天性心脏病手术后磁共振检查

目的 评价磁共振对手术后复杂先天性心脏病的诊断价值和检查技术。资料与方法 75例手术后复杂先天性心脏病作了磁共振检查，扫描序列为自旋回波T1WI序列，梯度回波电影序列和造影增强的磁共振血管成像序列。结果 75例中，法洛四联症等病变作右室流出道补片25例，其中7例补片远端吻合口狭窄，23例为Fontan或Glenn一类手术后，5例吻合口有梗阻。12例为主动脉弓病变术后，3例有残余梗阻，75例磁共振均清晰显示术后改变。结论 磁共振对手术后复杂先心病有很高的诊断价值，其中造影增强的磁共振血管成像序列必不可少。放射科医生熟悉手术方法对检查十分重要。     

Disparity between ratios of diameters and blood flows in central pulmonary arteries in postoperative congenital heart disease using MRI

PURPOSE: To compare the relative severity of stenoses of right or left pulmonary arteries with differences in flow to each lung after repair of congenital heart disease (CHD). MATERIALS AND METHODS: A total of 15 patients with postoperative congenital heart disease underwent MRI to evaluate branch pulmonary artery stenoses. Spin-echo images and MR angiography were used to assess morphology, and velocity-encoded cine (VEC) MRI was used to measure flow in the right and left pulmonary arteries. The ratios of the narrowest diameters of the right to left pulmonary arteries (R/L size) and right to left pulmonary arterial flow (R/L flow) were compared using Spearman's correlation. F test was used to assess the significance of the regression coefficients. RESULTS: R/L size ratio varied from 0.50 to 2.66, while the R/L flow ratio varied from 0.36 to 12.02. There was an exponential relationship between R/L size and R/L flow, with r2=0.78 and P=0.001. However, severity of morphologic stenoses was not clinically useful for predicting flow reduction. Prediction residuals ranged from -136% to 54% of the true R/L flow. CONCLUSION: Anatomical evaluation of the pulmonary arteries does not predict accurately differential blood flow in patients with pulmonary stenoses. Therefore, blood flow measurements are essential when considering the need for further surgical or interventional procedures.     

Assessment of vasculature using combined MRI and MR angiography

OBJECTIVE: The purpose of this study was to compare combined cine gradient-recalled echo MRI and MR angiography with conventional angiography in the evaluation of the pulmonary vascular supply in patients with pulmonary atresia, ventricular septal defect, and major aortopulmonary collateral arteries. MATERIALS AND METHODS: Eleven patients who underwent both MRI and conventional angiography were retrospectively reviewed. Contiguous 2D cine gradient-recalled echo images (TR range/TE, 30-80/4.8; flip angle, 20 degrees or 30 degrees ) and 3D MR angiographic images (TR range/TE range, 3.8-5.0/1.3-2.0; acquisition time, 13-32 sec) using gadopentetate meglumine (0.1-0.2 mmol/kg) were obtained. The presence, size, and course of the pulmonary arteries (main, right, left) and major aortopulmonary collateral arteries (>/= 5 mm) were determined. Presence of minor collateral arteries (< 5 mm) was also noted. Results were compared with findings at conventional angiography. RESULTS: MRI showed all main (n = 4) and branch (n = 17) pulmonary arteries found at conventional angiography and showed the pulmonary confluence in five of six cases. MRI showed all major aortic collaterals (n = 22) with a highly significant correlation between MRI and conventional angiography measurements (r = 0.84, p < 0.001 [95% confidence interval, -0.35 to 0.40]). One coronary artery collateral was not shown on MRI examination. At MRI, 12 of 14 major and four of seven minor brachiocephalic artery collaterals were shown. MRI showed more minor aortic collaterals than angiography (22 vs 18 vessels, respectively). CONCLUSION: Combined cine gradient-recalled echo MRI and MR angiography is a reliable method for imaging pulmonary vascular supply in patients with these disorders. Additional prospective studies comparing MRI and conventional angiography may determine whether routine preoperative conventional angiography is required.     

Pulmonary MR angiography and perfusion imaging—A review of methods and applications

The pulmonary vasculature and its role in perfusion and gas exchange is an important consideration in many conditions of the lung and heart. Currently the mainstay of imaging of the vasculature and perfusion of the lungs lies with CT and nuclear medicine perfusion scans, both of which require ionizing radiation exposure. Improvements in MRI techniques have increased the use of MRI in pulmonary vascular imaging. Here we review MRI methods for imaging the pulmonary vasculature and pulmonary perfusion, both using contrast enhanced and non-contrast enhanced methodology.In many centres pulmonary MR angiography and dynamic contrast enhanced perfusion MRI are now well established in the routine workflow of patients particularly with pulmonary hypertension and thromboembolic disease. However, these imaging modalities offer exciting new directions for future research and clinical use in other respiratory diseases where consideration of pulmonary perfusion and gas exchange can provide insight in to pathophysiology.     

evaluation of communication between intracranial arachnoid cysts and cisterns with phase-contrast cine MR imaging

BACKGROUND AND PURPOSE: The demonstration of communication between arachnoid cysts (ACs) and the adjacent subarachnoid space is a prerequisite for their proper management. CT cisternography (CTC) is the conventional method for functional evaluation of ACs. The sensitivity of MR imaging to CSF flow has been demonstrated, but reports of the clinical usefulness of MR CSF flow techniques in this application are limited. The purpose of our study was to prospectively evaluate the accuracy of MR CSF flow study as an alternative to CTC in this setting. METHODS: MR CSF flow study with retrospective ECG-gated 2D, fast low-angle shot, phase-contrast (PC), cine gradient-echo sequence was performed in 39 patients with an intracranial AC. Results were compared with intraoperative and CTC findings. RESULTS: PC cine MR imaging results were compatible with operative or CTC findings in 36 (92.3%) of 39 patients. Twenty-four cysts were noncommunicating, and 15 were communicating. Three cysts were evaluated as being noncommunicating on PC cine MR imaging (false-negative) but demonstrated contrast enhancement on CTC. No false-positive diagnoses occurred. All cysts regarded as being communicating on PC cine MR imaging were also found to be communicating on both confirmation methods. CONCLUSION: MR CSF flow imaging with a PC cine sequence can be incorporated in the imaging work-up of ACs. This is a reliable alternative to invasive CTC for the functional evaluation of ACs.     

Anomalous origin of the right pulmonary artery from the ascending aorta: Diagnosis by magnetic resonance imaging

Anomalous origin of the right pulmonary artery from the ascending aorta is a rare congenital anomaly. Magnetic resonance imaging (MRI) was performed on three patients with anomalous origin of the right pulmonary artery from the ascending aorta. ECG-gated, Tlweighted, spin-echo MRIs and cine MRIs were obtained. In one patient, postoperative MRI was also obtained. Echocardiography and cardiac catheterization were performed in three patients and angiocardiography was performed in two. MRI clearly showed anomalous origin of the right pulmonary artery from the posterior aspect of the ascending aorta, as well as combined anomalies including patent ductus arteriosus, aortopulmonary window, and interruption of the aortic arch in all three patients. Echocardiography missed this anomaly in all three. We suggest that MRI is an accurate imaging modality in diagnosing anomalous origin of the right pulmonary artery from the ascending aorta, obviating the need to perform angiocardiography     

Ex vivo evaluation of ferromagnetism,heating, and artifacts produced by heart valve prostheses exposed to a 1.5-T MR system

Ex vivo testing techniques were used to determine the ferromagnetic qualities of, presence of heating in, and artifacts produced by 13 different heart valve prostheses exposed to a 1.5-T (64-MHz) magnetic resonance (MR) system. None of the heart valve prostheses showed a measurable deflection in the 1.5-T static magnetic field. Only minimal artifacts were produced during MR imaging with a fast spoiled GRASS (gradient-recalled acquisition in the steady state) pulse sequence. The largest temperature changes measured during a “worst case” MR imaging sequence (estimated average specific absorption rate, 2.5 W/kg; estimated spatial peak specific absorption rate, 7.6 W/kg) were +0.2°C with the implant imaged “in air” and +0.3°C with the implant imaged in normal saline. Therefore, MR procedures performed with a 1.5-T (64-MHz) MR system may be performed safely in patients with any of the 13 different heart valve prostheses evaluated in this study.     

Assessment of chronic aortic dissection: contribution of different ECG-gated breath-hold MRI techniques

OBJECTIVE: Our objective was to evaluate the impact of different rapid MRI techniques for the assessment and follow-up of chronic aortic dissections. MATERIALS AND METHODS: Fifty-three patients (41 postoperative Stanford type A, 12 type B dissections) were scanned at 1.5 T during a 3-year period. The study reviewed ECG-gated breath-hold black blood sequences and 3D contrast-enhanced MR angiography of the thoracic aorta supplemented by segmented cine and phase-contrast imaging as well as abdominal contrast-enhanced MR angiography. A retrospective separate analysis of black blood acquisitions and contrast-enhanced MR angiograms from a total of 72 examinations was performed by two radiologists to evaluate detection of intimal flaps and assess image quality. RESULTS: Sensitivity and specificity of black blood sequences compared with those of contrast-enhanced MR angiography in detecting intimal flaps were 87% and 94% for the thoracic aorta, and 54% and 97% for the supraaortic branches, respectively. Contrast-enhanced MR angiography was subjectively rated as superior to black blood techniques for visualizing intimal flaps and yielded better overall image quality (p < 0.001). Aortic valve competence can be assessed on segmented cine techniques. Phase-contrast sequences enabled the quantification of regurgitant flow across the aortic valve and the analysis of flow patterns in the true and false channels. CONCLUSION: Contrast-enhanced MR angiography is superior to black blood MRI in detecting the presence or absence of intimal flaps and is particularly useful in assessing supraaortic branch vessel involvement. Cine and phase-contrast techniques should be included in the imaging follow-up to diagnose possible complications of chronic aortic dissections.     

Congenital diseases of the thoracic aorta. Role of MRI and MRA

Aortic malformations may be associated with other congenital heart abnormalities or may present independently, as incidental findings in asymptomatic patients. For more than 30 years, conventional imaging techniques for detection and assessment of congenital anomalies of the aorta have been chest X-ray, echocardiography and angiography. In recent times, considerable interest in congenital aortic diseases has been shown, due to technical progresses of noninvasive imaging modalities. Among them, magnetic resonance imaging (MRI) almost certainly offers the greatest advantages, especially in young patients in which a radiation exposure must be avoided as much as possible. MRI provides an excellent visualization of vascular structures with a wide field of view, well suited for evaluation of the thoracic aorta malformations. With the implementation of magnetic resonance angiography (MRA) it is also possible to depict any relationship with supra-aortic or mediastinal vessels. Phase contrast technique allows identification of the hemodynamic significance of the aortic alteration. Some technical considerations, which include fast spin-echo, gradient-echo and, especially, MRA techniques with phase-contrast and contrast enhanced methods, are discussed and applied in the evaluation of congenital thoracic aorta diseases.     

Quantification of flow dynamics in congenital heart disease: applications of velocity-encoded cine MR imaging.

Velocity-encoded cine (VEC) magnetic resonance (MR) imaging is a valuable technique for quantitative assessment of flow dynamics in congenital heart disease (CHD). VEC MR imaging has a variety of clinical applications, including the measurement of collateral flow and pressure gradients in coarctation of the aorta, differentiation of blood flow in the left and right pulmonary arteries, quantification of shunts, and evaluation of valvular regurgitation and stenosis. After surgical repair of CHD, VEC MR imaging can be used to monitor conduit blood flow, stenosis, and flow dynamics. There are some pitfalls that can occur in VEC MR imaging. These include potential underestimation of velocity and flow, aliasing, inadequate depiction of very small vessels, and possible errors in pressure gradient measurements. Nevertheless, VEC MR imaging is a valuable tool for preoperative planning and postoperative monitoring in patients with CHD.